Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6818. Adviser: Nancy Makri. Includes bibliographical references (leaves 83-85). Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6871. Adviser: Eduardo Fradkin. Includes bibliographical references (leaves 180-191) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph. D.)--Cornell University, 2007. / (UMI)AAI3276765. Source: Dissertation Abstracts International, Volume: 68-08, Section: B, page: 5311. Adviser: Sol Gruner.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6455. Adviser: Munir Nayfeh. Includes bibliographical references (leaves 103-109) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6463. Adviser: Yia-Chung Chang. Includes bibliographical references (leaves 104-109) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6464. Adviser: Yoshitsugu Oono. Includes bibliographical references (leaves 106-111) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2006. / "Title from dissertation home page (viewed June 28, 2007)." Source: Dissertation Abstracts International, Volume: 67-06, Section: B, page: 3202. Adviser: Shyh-Yuan Lee.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1058. Includes bibliographical references (leaves 78-81) Available on microfilm from Pro Quest Information and Learning.

Singlet fission is a multiple-exciton-generation process found in organic materials that could help to enhance the efficiency of future photovoltaic devices, by overcoming the Shockley-Queisser limit. In spite of considerable experimental and theoretical attention, different aspects of the process are still not fully understood. The main reason for this is that singlet fission is characterised by a complex interplay of electronic states, vibrational modes and electrostatic screening effects. In this thesis we employ \emph{ab initio} electronic structure techniques to study the excitations involved in fission in molecular crystals and dimers, using the well-studied pentacene molecule as a reference system. Linear-scaling density functional theory (LS-DFT) is used to model the influence of the crystal environment on charge-transfer (CT) configurations in the pentacene molecular crystal. We derive a general dipole correction scheme that allows us to eliminate finite-size effects from the calculations. We find that CT energies are significantly lowered by the response of the crystal environment, bringing them close to the energies of local excitations. This result lends support to the idea that the photoexcited precursor state to fission has significant CT character, and emphasises the role played by CT configurations in fission in the crystal. Furthermore, we use DFT to parametrise a linear vibronic coupling Hamiltonian of a covalent dimer of pentacene, forming the basis for many-body quantum dynamics calculations of the interplay between electronic and vibrational degrees of freedom. This reveals an interesting role for symmetry in fission in such dimers. Due to their high symmetry, couplings that could enable fission are precluded at the ground-state geometry. However, dynamic symmetry breaking by vibrational modes opens up an efficient pathway for fission, via an avoided crossing mediated by virtual CT configurations. Finally, we explore the influence of different side-groups and solvent environments on fission in pentacene dimers. To this end, we employ DFT with both implicit and explicit solvent models, combined with large-scale calculations to achieve sufficient sampling of solvent-solute configurations.

<p> I discuss the design and operation of a system for levitating a charged, &mu;m-scale, multilayer graphene nanoplatelet in a quadrupole electric field trap in high vacuum. Levitation decouples the platelet from its environment and enables sensitive mechanical and magnetic measurements. </p><p> First, I describe a method of generating and trapping the nanoplatelets. The platelets are generated via liquid exfoliation of graphite pellets and charged via electrospray ionization. Individual platelets are trapped at a pressure of several hundred mTorr and transferred to a trap in a second chamber, which is pumped to UHV pressures for further study. All measurements of the trapped platelet's motion are performed via optical scattering. </p><p> Second, I present a method of gyroscopically stabilizing the levitated platelet. The rotation frequency of the platelet is locked to an applied radio frequency (rf) electric field <i><b>E</b></i>_rf. Over time, frequency-locking stabilizes the platelet so that its axis of rotation is normal to the platelet and perpendicular to <i><b>E</b></i>_rf. </p><p> Finally, I present optical data on the interaction of a multilayer graphene platelet with an applied magnetic field. The stabilized nanoplatelet is extremely sensitive to external torques, and its low-frequency dynamics are determined by an applied magnetic field. Two mechanisms of interaction are observed: a diamagnetic polarizability and a magnetic moment proportional to the frequency of rotation. A model is constructed to describe this data, and experimental values are compared to theory.</p><p>